XBAR Split-Ladder Filters With Variable Pitch for Spurious Mode Control

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing RF filters are not well-suited for higher frequencies and bandwidths required by future communications networks, particularly in 5G NR and WiFi bands, due to limitations in tuning range and spurious modes.

Innovation Solution

A split-ladder architecture is employed, where series and shunt resonators are fabricated on separate chips with different piezoelectric layer thicknesses and dielectric layers to achieve the desired frequency separation, using transversely-excited film bulk acoustic resonators (XBARs) with varying pitch and mark to optimize resonance and anti-resonance frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If existing acoustic wave resonators (SAW, BAW, FBAR) are used in RF filters, then the filters can operate at current communication frequencies, but they cannot handle the higher frequencies and wider bandwidths required for future 5G NR and WiFi networks

Engineering Contradiction:

Improveoperating frequencyVSAvoidperformance at higher frequencies

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The resonator is divided into multiple sub-resonators with different pitch values. Each sub-resonator contributes to different frequency components, enabling the overall resonator to achieve wider bandwidth and higher frequency operation while maintaining control over spurious modes through the specific pitch variations

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the resonator structure have different local properties - specifically, sub-resonators have different pitch values and the piezoelectric layer has varying thickness in different regions. This local variation enables tailored frequency response and suppression of spurious modes at specific frequency locations

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If conventional resonator designs are used, then manufacturing is straightforward, but tuning range is limited and spurious modes cannot be effectively controlled

Engineering Contradiction:

Improvetuning rangeVSAvoidspurious modes

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The invention changes key physical parameters of the resonator - specifically the pitch of sub-resonators and the thickness of the piezoelectric layer. By varying these parameters across different sub-resonators, the design achieves extended tuning range and controlled suppression of spurious modes through destructive interference at unwanted frequencies

Inventive Principle:

Principle #35Parameter changes

3Speed

If higher frequency operation is implemented in existing resonator types, then bandwidth increases, but spurious modes become more problematic

Engineering Contradiction:

ImprovefrequencyVSAvoidspurious modes

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The invention converts the potentially harmful spurious modes into beneficial elements by designing sub-resonators whose spurious modes intentionally overlap and interfere destructively at specific frequency locations. This transforms what would normally be harmful artifacts into a mechanism for achieving stopband rejection and controlling the frequency response

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution enables RF filters to handle higher frequencies and wider bandwidths with reduced spurious modes, improving performance and reliability in 5G NR and WiFi applications.

Implementation Method 1

a piezoelectric layer having a front surface and a back surface

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

transversely-excited film bulk acoustic resonators (XBARs) with varying pitch and mark to optimize resonance and anti-resonance frequencies

Methodology Applied

Scientific EffectAcoustic wave resonance: Resonance

Data Source

PatentUS12375062B2Transversely-excited film bulk acoustic resonator filters with sub-resonators having different mark and pitch

Publication Date: 2025.07.29 MURATA MFG CO LTD

AI summary

Radio frequency filters are disclosed. A bandpass filter is discloses that includes one first bulk acoustic resonator on a first chip including a first piezoelectric layer having an LN-equivalent thickness less than or equal to 535 nm; a second bulk acoustic resonator on a second chip including a second piezoelectric layer having a thickness greater than the LN-equivalent thickness of the piezoelectric layer on the first chip; and a circuit card coupled to the first chip and the second chip and that electrically connects the first chip to the second chip.